The present invention relates to a joint structure which can be applied to a joint mechanism of a mechanical apparatus such as a robot arm, and the robot arm including the joint structure.
Conventionally, in a structure of a multiple-joint robot arm, an actuator which drives a joint is usually arranged in a joint portion or near the joint portion. However, in such a structure, hand inertia becomes large, because a heavy motor or the like is arranged near a hand such as a wrist of a human-like arm. This may hinder an improvement of hand position control performance, or may generate a large impact in collision, which requires a consideration in terms of safety.
In response to the above issue, a wire drive type robot arm has been developed, in which the actuator is arranged near a base end position away from the driven joint and driving force is transmitted by wire. Because the hand can be slimmed down in the wire drive type robot arm, the wire drive type robot arm has excellent characteristics such as high-speed drive.
However, in the wire drive type robot arm, in the case where the wrist portion is driven by arranging the actuator in a body portion which is of a base portion to which the arm is attached in order to reduce the hand-side inertia, namely, in the case where a run distance of the wire is made longer, it is necessary that the wire be arranged beyond the joint such as an elbow of the human-like arm. In this case, when driving the joint located in the midway of the wire, a wire path length changes, which causes an issue that the change in wire path length influences on joint movement of the end portion, such as the wrist, which is driven by the wire.
In order to solve the issue, Patent Document 1 (Japanese Patent No. 3290709) discloses a configuration in which a pair of pulleys is arranged so as to be displaced from a rotation center of the joint. Further, Patent Document 2 (Japanese Examined Patent Publication No. H6-77914) discloses a configuration having a wire guide pulley the rotation center is rotated in accordance with the joint movement.
However, in the configuration disclosed in the Patent Document 1, the change in wire path length by the joint movement cannot completely be eliminated, so that the change in wire path length is increased as a rotation angle of the joint located in the midway is increased. Further, in the configuration disclosed in the Patent Document 2, when the rotational movement of the wire guide pulley is generated in accordance with the joint rotation, in the state where the joint is bent, the wire path is bent toward a direction opposite to the direction of a front end-side arm member before the wire is bent toward the direction of the front end-side arm member. Therefore, the wire path cannot be kept completely constant irrespective of the joint movement.
An object of the present invention is to provide, in order to solve the above issues, a joint structure which can transmit driving force without being influenced by rotating movement at the revolute joint at all, and the robot arm including the joint structure.